1. Technical Field
The present invention relates to a technology for compensating for inconsistencies in ink density in a device that outputs a dot matrix.
2. Related Art
An image-forming device having an ink ejecting mechanism, such as an ink jet printer, has a plurality of nozzles, each for ejecting an ink dot in a droplet form, so as to perform high-speed printing. Ideally, the nozzles are spaced apart at precise intervals. However, in practice such nozzles tend not to be spaced apart at exactly correct intervals due to fabrication errors. Furthermore, a problem exists of a possible inconsistency in a volume of an ejected ink droplet. As a result of these problems images formed by ejected ink droplets may suffer from anomalies in position or size due to uneven ink dispersion. In other words, an image formed by ink droplets ejected from nozzles may suffer from deficiencies resulting from fabrication errors in nozzles. Particularly, in a so-called “one-pass printer” such as a line head printer that scans a print medium in a single direction, uneven dispersion can give rise to “banding”.
To prevent banding, there are several known techniques that can be applied in image processing. For example, JP-A-1-129667, JP-A-3-162977, and JP-A-5-057965 disclose such technologies. JP-A-1-129667 discloses a technology for compensating for banding by using a calibration table. In JP-A-1-129667, an image-forming device stores a calibration table that includes calibration coefficients. The calibration coefficients are obtained by measuring printed densities of dots formed by a pattern, with all of the dots having a maximum density. When an image is formed, the corresponding calibration coefficient is multiplied to an appropriate pixel value. Thus, the inconsistencies in density are compensated for. JP-A-3-162977 discloses a linear calibration as well as the technology disclosed in JP-A-1-129667. JP-A-5-057965 discloses compensation using a plurality of calibration tables.